1. Field of the Invention
This invention relates to fluid operated conduit cleaning systems and, more particularly, to a valve unit for producing high volume, high pressure, pulsed delivery of a fluid, as for introduction into a conduit for purposes of cleaning the inside passage thereof.
2. Background Art
Opening of blocked and silted drainage, sewer and other conduits is a vexatious problem that has plagued the industry for many years. It is not uncommon for conduits to run uninterrupted for hundreds of feet without any access structure for cleanout. To further aggravate the problem, these conduits may have one or more sharp bends, which makes conventional rodding techniques inadequate. A still further problem is that frequently the obstructing material will be positively adhered to the inside conduit surface. The use of a flexible rod may do nothing more than bore a restricted opening through the obstruction which thereby allows only a limited flow volume.
To overcome the above problems, systems employing high pressure fluid have been used. One such system employs a flexible hose with a nozzle having one or more passageways to produce a continuous, rearwardly expelled fluid jet Such a system is shown in U.S Pat. No. 1,176,518, to Burns Fluid is delivered under pressure through the nozzle and directed thereby angularly outwardly with respect to the axis of the conduit. The high pressure discharging fluid serves two primary functions--1) it effectively advances the hose through the conduit and around sharp turns; and 2) it scours the inside of the conduit wall to maximize the area of the flow passageway. While the above system has proven very effective, its principal drawback is that the nozzle may not be able to penetrate or dislodge a tightly packed obstruction.
To overcome the last mentioned problem, it is known to provide an additional nozzle passageway to generate a forwardly facing, high pressure fluid jet, as shown in the above-noted Burns '518 patent, to blast through the obstruction. It is possible with conventional technology to employ this type of system to penetrate blocked and heavily silted lines up to as much as 400 feet in length. These systems are generally adequate for most industrial, municipal, and household applications through manhole access. However, this system may not be adequate where curves, elbows, and traps are encountered and/or when the conduit length significantly exceeds 400 feet.
In order to enhance advancement of the nozzle, particularly through a circuitous conduit pathway, and breakup of obstructions, it is known to interrupt the nozzle flow to produce a pulsed fluid delivery through the nozzle. It is a known principal that repetitive interruption of high pressure flow through a nozzle to cause a pulsating action will result in the nozzle and hose continuing to progress through a conduit and over or around obstructions more effectively than can be achieved by the steady pull obtained from a constant rearward expulsion of fluid.
Several different mechanisms are known in the art for producing pulsed delivery of a fluid. One such system is shown in U.S. Pat. No. 4,838,768, to Flaherty. Flaherty employs two pistons which alternatingly operate to discharge fluid through an outlet. Pulses from the separate pistons are timed to immediately follow one another. It is also possible to disable one of the pistons to provide a lag between successive pulses by a single one of the pistons.
The Flaherty system is relatively complicated. For example, there are five check valves on the system and multiple moving pistons Failure of any element may result in system malfunction. Another problem with the Flaherty system is that it is inherently quite cumbersome by reason of there being multiple pistons and flow passageways associated therewith. It is a desirable objective of planners of such systems to minimize their size, due to the fact that most such systems are regularly transported and used in the field
Another prior art system is shown in U.S. Pat. No. 1,796,941, to Pottenger, Jr. Pottenger, Jr. has a valve that repetitively repositions to vary the discharge of fluid through an outlet. Pottenger, Jr. notes on page 2, beginning at lines 126 of his patent, that the valve, in operation, never fully seats. Resultingly, there is no sharp transition between pulse and no-pulse conditions, which is desirable to effect positive advance of a nozzle through a conduit. Instead, Pottenger, Jr. merely produces a pressure that increases and decreases to cause an even radial distribution of water, as in a sprinkler system such as that shown in the Pottenger, Jr. patent.
A further prior art device is shown in U.S. Pat. No. 1,218,567, to Kellan. Kellan also employs a reciprocating closure which alternatingly seats and unseats to produce pulsed delivery of an incoming supply of fluid to a point of use. One drawback with Kellan is that once the closure is seated no additional water flows from the inlet towards the outlet. The result of this is the development of an air pocket immediately downstream of the closure. Upon the closure unseating, the volume and pressure of the pulse is reduced over what it would be in the absence of the air pocket. Pressure loss results in a less effective conduit cleaning and advancing action for a nozzle.